8250240: Address use of default constructors in the java.util.concurrent

Reviewed-by: martin, lancea

src/java.base/share/classes/java/util/concurrent/RecursiveTask.java

@@ -68,6 +68,11 @@ package java.util.concurrent;
 public abstract class RecursiveTask<V> extends ForkJoinTask<V> {
     private static final long serialVersionUID = 5232453952276485270L;
 
+    /**
+     * Constructor for subclasses to call.
+     */
+    public RecursiveTask() {}
+
     /**
      * The result of the computation.
      */